The present invention relates to an improved sub-surface, or in-ground/in-water, heat exchange apparatus for use in association with any heating/cooling system utilizing sub-surface heat exchange elements as a primary or supplemental source of heat transfer, as well as to improved methods of installing direct expansion sub-surface heat exchange tubing.
Ground source/water source heat exchange systems typically utilize fluid-filled closed loops of tubing buried in the ground, or submerged in a body of water, so as to either absorb heat from, or to reject heat into, the naturally occurring geothermal mass and/or water surrounding the buried or submerged tubing. Water-source heating/cooling systems typically circulate water, or water with anti-freeze, in plastic underground geothermal tubing so as to transfer heat to or from the ground, with a second heat exchange step utilizing a refrigerant to transfer heat to or from the water, and with a third heat exchange step utilizing an electric fan to transfer heat to or from the refrigerant to heat or cool interior air space.
Direct expansion ground source heat exchange systems, where the refrigerant transport lines are placed directly in the sub-surface ground and/or water, typically circulate a refrigerant fluid, such as R-22, in sub-surface refrigerant lines, typically comprised of copper tubing, to transfer heat to or from the sub-surface elements, and only require a second heat exchange step to transfer heat to or from the interior air space by means of an electric fan. Consequently, direct expansion systems are generally more efficient than water-source systems because of fewer heat exchange steps. Further, because copper is a better heat conductor than most plastics, and since the refrigerant fluid circulating within the copper tubing of a direct expansion system generally has a greater temperature differential with the surrounding ground than the water circulating within the plastic tubing of a water-source system, generally, less excavation and drilling is required, and installation costs are lower, with a direct expansion system than with a water-source system.
While most in-ground/in-water heat exchange designs are feasible, various improvements have been developed intended to enhance overall system operational efficiencies. Several such design improvements are taught in U.S. Pat. No. 5,623,986 to Wiggs, and in U.S. Pat. No. 5,816,314 to Wiggs, et al., the disclosures of which are incorporated herein by reference. These prior designs basically teach the utilization of a spiraled fluid supply line subjected to naturally surrounding geothermal temperatures, with a fully insulated fluid return line. However, because only the fluid return line is insulated, and because both the supply and return lines are all the same size, without a dedicated smaller-sized refrigerant liquid/fluid transport line and a dedicated larger-sized refrigerant vapor/fluid transport line so as to facilitate appropriate refrigerant supply and return capacity in a deep well (greater than 100 feet deep) direct expansion application, these prior designs are intended for a near-surface (within about 25 to 100 feet of the surface) direct expansion system application, when operating in a reverse cycle mode. Further, these prior art designs do not provide for a dedicated liquid/fluid line trap, in conjunction with a dedicated liquid line and a dedicated vapor line, so as to assist in preventing refrigerant vapor from migrating into the refrigerant liquid line and decreasing system operational efficiencies.
Other vertically oriented geothermal heat exchange designs are disclosed by U.S. Pat. No. 5,461,876 to Dressler, and by U.S. Pat. No. 4,741,388 to Kuriowa. Dressler's '876 patent teaches the utilization of several designs of an in-ground fluid supply and return line, with both the fluid and supply lines shown as being the same size, and not distinguished in the claims, but neglects to insulate either the fluid return line or the fluid supply line, thereby subjecting the heat gained or lost by the circulating fluid to a “short-circuiting” effect as the supply and return lines come into close proximity with one another at various heat transfer points. Dressier also discloses the alternative use of a pair of concentric tubes, with one tube being within the core of the other, with the inner tube surrounded by insulation or a vacuum. While this multiple concentric tube design reduces the “short-circuiting” effect, it is practically difficult to build and maintain and could be functionally cost-prohibitive, and it does not have a dedicated liquid line and a dedicated vapor line with a liquid line trap. Kuriowa's preceding '388 patent is similar to Dressler's subsequent spiral around a central line claim, but better, because Kuriowa insulates a portion of the return line, via surrounding it with insulation, thereby reducing the “short-circuiting” effect. However, Kuriowa does not have a dedicated liquid line and a dedicated vapor line with a liquid line trap. The lowermost fluid reservoir, claimed by Kuriowa in all of his designs, can work in a water-source geothermal system, but can be functionally impractical in a direct expansion sub-surface system, potentially resulting in system operational refrigerant charge imbalances, compressor oil collection/retention problems, accumulations of refrigerant vapor pockets due to the extra-large interior volume, and the like. Kuriowa also shows a concentric tube design preceding Dressler's, but it is subject to the same problems as Dressler's. Further, both the Dressler and Kuriowa designs are impractical in a reverse-cycle, deep well, direct expansion system operation since neither of their primary designs provide for, or claim, an insulated smaller sized liquid line and an un-insulated larger sized vapor line, which are necessary to facilitate the system's most efficient operational refrigerant charge and the system's compressor's efficient refrigerant supply and return capacities.
Generally, a design which insulates the supply line from the return line and still permits both lines to retain natural geothermal heat exchange exposure, such as a thermally exposed, centrally insulated, geothermal heat exchange unit, as taught by Wiggs in U.S. patent application Ser. No. 10/127,517, which is incorporated herein by reference, would be preferable over non-insulated lines and over designs which insulate a portion of one sub-surface line. However, while the device in Wiggs' '517 application is an improvement over prior art, in a sub-surface soil application, it could still be subject to some minor short-circuiting effects and to some potentially adverse vapor formation in the un-insulated liquid line at undesirable locations or times.
In a direct expansion system, the supply and return refrigerant lines may be defined depending on whether the refrigerant transport line is supplying refrigerant to the compressor unit from the ground, i.e. a supply line, or is returning refrigerant from the compressor to the ground, i.e. a return line. Conversely, the operatively connected refrigerant transport line supplying refrigerant to, or returning refrigerant from, the interior air handler, which is also operatively connected via refrigerant transport lines to the compressor unit, would have the opposite designation, being designated as a return line from the air handler in the heating mode, and as a supply line to the air handler in the cooling mode, as is well understood by those skilled in the art. In the heating mode the ground is the evaporator, and in the cooling mode, the ground is the condenser.
For purposes of this present invention, supply and return lines are defined based upon whether, in the heating mode, warmed refrigerant vapor is being supplied to the system's compressor, after acquiring heat from the sub-surface elements, in which event the larger interior diameter vapor/fluid line is the supply line and evaporator, and the smaller interior diameter liquid/fluid line operatively connected to the interior air handler is the return line; or whether, in the cooling mode, hot refrigerant vapor is being returned to the sub-surface elements from the system's compressor, in which event the larger interior diameter vapor/fluid line is the return line and condenser, and the smaller interior diameter liquid/fluid line is the supply line, via supplying cooled liquid refrigerant to the interior air handler.
None of the prior art described above addresses an improved means of designing a direct expansion system for a reverse-cycle heating/cooling system operation via insulating only one smaller interior diameter line, designed primarily for liquid/fluid refrigerant transport, which smaller line may be utilized as a return line in the heating mode and as a supply line in the cooling mode, and of not insulating at least one, or two or more combined, larger interior diameter lines, designed primarily for vapor/fluid transport, which can provide expanded surface area thermal heat transfer as supply lines in the heating mode and as return lines in the cooling mode. While at least two, larger combined interior diameter, vapor/fluid refrigerant transport lines, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant transport line would generally be preferable because of the resulting expanded heat transfer surface contact area, instances may arise where only one, larger interior diameter, vapor/fluid refrigerant line, operatively connected to one, smaller interior diameter, liquid/fluid refrigerant line could also be preferable, or where a larger interior diameter vapor/fluid refrigerant line is spiraled around a centrally located, insulated, smaller diameter liquid/fluid refrigerant line could be preferable.
An example of where only one, larger interior diameter, vapor/fluid refrigerant line, operatively connected to only one, smaller interior diameter, liquid/fluid refrigerant line could be preferable would be in a near-surface horizontal, or less than vertical, application. In such an application, where surface land area was sufficient, the expense of well-drilling, or the expense of a large surface area excavation, could be avoided by simply excavating a trench, several inches to one foot in width and about three to four feet in depth below the maximum frost/heat line, via a backhoe or a trenching machine, and simply installing/inserting the lines and backfilling. In such a simplified application, which also eliminates the necessity to connect multiple, often ten or more, heat transfer lines in a horizontal wide-area matrix, as with conventional near-surface direct expansion systems, a liquid trap should also be installed at the point, within the sub-surface location, that is below the point at the end of the refrigerant lines where the insulated liquid line connects to the un-insulated vapor line.
Where a close to zero-tolerance short-circuiting effect is desirable, and where the time and expense of constructing other designs, such as a concentric tube within a tube, or a spiraled single fluid return line and single fluid supply line of the same sized interior diameters, could be financially, or functionally and/or efficiently, prohibitive in a sub-surface direct expansion application, and where the thermal exposure area of a single geothermal heat transfer line, or tube, could be too centralized and too heat transfer restrictive, a system design improvement would be preferable which incorporated a cost-effective installation method, capable of operating in a reverse-cycle mode in a sub-surface direct expansion application, with close to zero-tolerance short-circuiting effect, with expanded sub-surface heat transfer surface area capacities, and with a liquid refrigerant trap means at the bottom of the sub-surface heat exchange lines to assist in preventing refrigerant vapor migration from the refrigerant vapor line into the refrigerant liquid line.